Diurnal rhythm in serum leptin

Aim: To assess 24-hour serum leptin levels in children. Subjects and methods: Five girls and two boys aged 10.4-13.6 (mean 12.2) ye ars with pubertal stages I to III were studied. All children were healthy. A fasting blood sample was drawn at 08.00 hours, and thereafter samples wer e obtained every 2 hours throughout 24 hours until 08.00 hours the next mor ning. Serum leptin was measured by a specific radioimmunoassay, Results: A statistically significant circadian variation was found in mean leptin profile expressed as a percentage of overall day mean (F-ratio=10.4; P<0.001) with trough and peak levels (+/- SEM) at 10.00 (6.55 +/- 1.52 mg/ l) and 24.00 hours (10.99 +/- 2.34 mg/l), respectively. Conclusions: In normal children serum leptin levels exhibit a nocturnal inc rease and a decrease during the morning. The nocturnal rise may represent a time lagged stimulating effect of insulin. The diurnal rhythm needs to be considered when serum leptin is assessed in clinical studies.